This invention relates to electric components in general and more particularly, to the construction of a spark gap component, that, during operation, is mounted within a protective shield that surrounds it. The spark gap component and the protective shield are separated by a solid dielectric. These spark gap components are used as auxiliary spark gaps for spark plugs, particularly in motor vehicles.
A spark gap component known in the art comprises a tubular insulator and two electrodes, with one electrode mounted in a vacuum-tight manner on one end of the insulator, and the second electrode mounted on the other end of the insulator. When in operation, one electrode has a potential different from ground while the other electrode has a potential near that of ground. Both of the electrodes have an essentially flat active surface. These flat surfaces are provided with a layer of fire-resistant material. This spark gap component is used in a spark plug connector. In its assembled state, the component is located within a bore in an insulating body that is covered by a metallic shield. The ignition voltage of the spark gap component is approximately 8 to 10 kV, as disclosed in DE-B-24 18 261.
Other spark gap components that have been designed for even higher ignition voltages are known in the art. In order to ensure, among other things, the long-term stability of the ignition voltage when it is in the range of 2 to 16 kV, the active parts of the electrodes are made of titanium, zirconium and similar metals, and the spark gap component is filled with an inert gas at a pressure of 0.8 to 10 bar, as disclosed in U.S. Pat. No. 3,956,657. In order to increase the ignition voltage to 18 kV, as well as for other reasons, another spark gap component known in the art provides an ignition aid that is attached to the inner wall of the insulator near the discharge gap. The sum of the spacings of the ignition aid from the rounded or bevelled electrode edges is greater than the spacing between the electrodes and is approximately 0.5 mm. This component, designated as an auxiliary spark gap, is essentially filled with nitrogen at a pressure of approximately 15 bar, as disclosed in EP-C-0 099 522.
It has been discovered that when using auxiliary spark gaps which have an ignition voltage increased to the range of 15 to 25 kV, which are then shielded, the ignition voltage deviates from and is considerably less than when the auxiliary spark gaps are unshielded.
In view of this discovery, there is a need for a spark gap component in which the ignition voltage is essentially independent of whether or not the spark gap component is subsequently shielded. In particular, when the spark gap component is shielded, the ignition voltage should not be considerably less than the ignition voltage when the spark gap component is not shielded.